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Thermochemical imaging of the Earth’s mantle: Global inversion of seismic waveforms, satellite gravity data and surface elevation

Periodic Reporting for period 1 - WINTERC-3D (Thermochemical imaging of the Earth’s mantle: Global inversion of seismic waveforms, satellite gravity data and surface elevation)

Reporting period: 2015-03-01 to 2017-02-28

Over the last few years, significant scientific efforts have been made to characterize the thermal and compositional structure of the Earth’s mantle through geophysical, geochemical and geological data interpretation, mineral physics experiments and numerical modelling. A reliable image of the thermochemical structure of the upper mantle is essential in order to understand fundamental processes including volcanism, seismic activity and the development and evolution of surface topography. In recent years, satellite missions orbiting the Earth are providing the scientific community with a wealth of data with unprecedented resolution. These data, are yet to be fully exploited in terms of imaging the solid Earth. Modelling and interpretation of geophysical and petrological data sets provide a multifaceted image of the true thermochemical structure of the Earth that needs to be appropriately and consistently integrated. A simple combination of models computed using the different data sets is insufficient due to the non-uniqueness and different sensitivities of these models. An integrated, joint inversion of the different data types within a self-consistent framework that exploits the different sensitivity of the constraining data sets is required, and this is the fundamental aim of WINTERC-3D. WINTERC-3D is aimed to develop a method for an accurate, self-consistent joint inversion of seismic waveform data, satellite gravity and surface topography data within a self-consistent thermodynamic framework, and apply it to obtain a detailed and robust global thermochemical image of the lithosphere and underlying upper mantle. WINTERC-3D is leaded by J. Fullea and S. Lebedev, in the Dublin Institute for Advanced Studies (DIAS).
The use of a new type of measurement (GOCE satellite gradiometric data, initially intended to study the ocean circulation) to image the solid Earth is of great interest to the Earth Science community at present. The impact of WINTERC-3D in this sense is twofold: i) a new integrative approach to exploit these data and is provided to the scientific community; and ii) Space agencies and technology companies get feedback about on-board equipment specifications and general planning for future missions. As a future reference Earth model, WINTERC-3D will contribute to European excellence and competitiveness by providing thorough basis for global and regional studies ranging from the origin and evolution of the Earth to mantle convection, dynamics of plate tectonics, and to ore and diamond resource assessment and prospecting.

A unique aspect of this proposal is the significant enhancement of the use of a new class of satellite observation data. Showing the ability of these remote sensing data to illuminate the solid Earth (with society-relevant implications for basic dynamic processes responsible for global seismicity, volcanism, and for natural resource assessment) has important outreach potential for a broad audience (“How deep inside the Earth can we see from a satellite?”). The communication and public engagement strategy of WINTERC-3D are designed so as to appropriately deliver this potential to society in the form of outreach activities.
A preliminary global reference temperature and density model (SL_TER_ref) has been derived using an initial mantle composition regionalization based on the global shear-wave SL2013sv model and global average compositions of xenoliths/peridotite massifs from different tectonothermal ages. The inversion is constrained by thermodynamically self-consistent Temperature-Pressure tables pre-calculated using the computational petrology software package Perple_X (

A parallelized integrated geophysical-petrologocal software to invert seismic waveform data (WINTERC) has been developed and tested with synthetic data sets. WINTERC runs a forward solver where all relevant rock physical properties modelled are computed within a thermodynamically self consistently framework allowing for a direct parameterization of the thermochemical conditions within the Earth. The 3D waveform data have been transformed into phase velocity dispersion curves for both Rayleigh and Love surface-waves that can be modelled in 1D beneath each particular geographical location.

WINTERC inverts the dispersion curves along with surface topography and heat flow using a non-linear gradient search algorithm. The parameter space comprises crustal structure, mantle structure and seismic radial anisotropy. To handle the very complex parameter space a further inversion for the dumping parameters themselves is carried out in the regularization.

A global gravity solver built on spherical harmonic formalism (GGSH) has been developed to compute synthetic gravity observables based on any given 3D distribution with the Earth. The next step consists on inverting satellite and terrestrial gravity data for the composition of the upper mantle assuming (or strongly dumping towards) the temperature distribution constrained by the seismic, elevation and heat flow data. The resulting 3D temperature and compositional model will be tested against appropriate 3D forward solvers to enforce internal consistency of all constraining data sets and its uncertainty will be assessed through selective Monte Carlo analysis and projection subspaces grids.
The preliminary results of WINTERC-3D have been presented in different workshops and conferences including four invited talks. Javier Fullea taught a short course on “Satellite data for studying the lithosphere” in the framework of the European Space Agency program to train young scientist, and taught another short course on “Integrated geophysical-petrological modelling” offered by DIAS to Irish undergraduate Earth Sciences students. J. Fullea also acted as a Marie Skłodowska-Curie ambassador in the European Researchers' Night (NIGHT) event “Night of the volcanoes: observing the Earth from the space” that took place in the Canary Islands, Spain (September, 2015). J. Fullea organized and convened a thematic session devoted to integrated lithospheric modelling at global scale in the largest international conference in Earth Sciences (AGU Fall meeting, 2016).

WINTERC-3D has represented an excellent platform to enhance the scientific career of J. Fullea in terms of leadership, networking and management skills. Based on the positive outcome of WINTERC-3D, J. Fullea has secured funding to support a research team of four postdoctoral scholars in DIAS working on complementary strands of integrated geophysical-petrological modelling of the Irish on- and off-shore crustal and mantle structure and evolution.

Furthermore, the outcomes of WINTERC-3D attracted the interest of other research groups in Europe, and as a result the research team of WINTERC-3D joined, as co-PI’s, an European Space Agency international project aimed at exploiting gravity and magnetic satellite data to explore the global structure and evolution of the Earth (“3D Earth, a dynamic, living planet”,
Fig.1: preliminary global temperature and density model (SL_TER_ref)
Fig.2: Temperature at 150 km depth from SL_TER_ref
Fig. 4: Sensitivity tests integrated inversion: projection subspaces
Fig. 3: WINTERC 1D inversion of waveforms, topography and SHF data
Fig. 5: Power spectra of satellite & synthetic (SL_TER_ref) gravity data